HER2-binding and anti-proliferative activity. (a) HER2-binding activity of MGAH22 was compared with RES120 or trastuzumab by antigen-capture enzyme-linked immunosorbent assay. EC50 (and 95% confidence interval) values were 39.33 (29.45 to 52.52) ng/mL for MGAH22 and 45.75 (33.37 to 62.67) ng/mL for RES120 (left panel) and 28.76 (24.96 to 33.15) for MGAH22 and 27.28 (23.6 to 31.53) ng/mL for trastuzumab (right panel). (b) Proliferation of JIMT-1 and SKBR-3 cells in the presence of MGAH22, RES120, or trastuzumab. Data are presented as mean ± standard error of the mean. EC50, effective concentration for 50% binding; MGAH22, chimeric anti-HER2 monoclonal antibody with an optimized Fc domain; Neg ctrl mAb, negative control monoclonal antibody; RES120, chimeric anti-HER2 monoclonal antibody with wild-type human immunoglobulin G 1 Fc domain; RLU, relative light units.